As medical technology has gotten amazingly advanced, and we've gained more and more control over how and when babies are born, we tend to think that as long as you're not extremely premature, it doesn't really matter exactly how long a baby cooks in its mother's womb. Well, think again. Two new studies have found that a lot can depend on when you're born—even if you're born during the period that's considered full term—and it can have long-lasting effects on things like your academic performance and mental health.

The first study looked at babies that fell within the 37 to 41 week period that most consider full term. You probably wouldn't think there'd be much difference in how children born during this period would end up doing in school, but think again. Researchers looked at 128,000 kids in the New York City public school system and found that whether kids were born at 37 weeks or 41 weeks mattered. By third grade, the kids born at 37 weeks were a third more likely to have severe difficulties in reading, and they also had a 19 percent greater chance of having moderate problems in math than those born at 41 weeks. Overall, the differences in the test scores between the two groups of kids were small but significant.

Researchers say these results should factor into how we decide which babies are considered premature, and they should also be considered in the ongoing debate about whether it's a good idea to allow pregnant women to schedule early C-sections for the purposes of convenience. Dr. Kimberly Noble, the study's lead author and an assistant pediatrics professor at Columbia University Medical Center, says expectant parents should "at least proceed with caution before electing to have an earlier term birth." There's no need to panic if your baby is born at 37 weeks, but people also should not be going out of their way to have them that early.

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If you go much earlier than 37 weeks, things get a bit more frightening. Another study, this one conducted by researchers at Kings College London, found that babies born prematurely were far more likely to suffer from mental health problems like schizophrenia, major depression, and bipolar illness. The researchers used birth and hospital records for more than 1.3 million people born in Sweden between 1973 and 1985, and they compared data from those born at full term and those born very premature (less than 32 weeks). They found the premature babies were more than twice as likely to land in the hospital for schizophrenia, three times as likely to have major depression, and a whopping seven times more likely to be bipolar.

Even if babies were not extremely premature but were instead born between 32 and 36 weeks, they were still at increased risk. They had a 60 percent higher chance of schizophrenia, they were 34 percent more likely to have major depression, and twice as likely to be bipolar. While all of these numbers sound terrifyingly large, do keep in mind that while the relative risk of mental illness is higher for preemies, the number of people that were actually hospitalized for any of those illnesses was still very low.

As for why there is a connection between being premature and having mental illness, researchers explained that the "preterm brain" is especially prone to injury, and MRIs of kids who were born very early have found that there are "disruptions in brain networks" that are like what you'd see in a psychiatric patient. It's also possible that there is some genetic factor that is triggered by being born early.

Of course, people don't generally opt to have premature births in the way they might to have an early C-section. So it's not as if you can warn people off against having their babies extremely early, but these findings are helpful in that they could lead to earlier or more careful mental health screenings for people who are born prematurely. And, taken together, this research seems to confirm what we already sort of knew: ideally you leave a baby in the womb for as long as is safely possible—as long as it's not too long, like two or three years long because that's just weird and probably very uncomfortable and sure to cause a whole host of other problems for the child's development.